Self-balancing potentiometer circuit having illuminated indicating dial



March 13, 1951 A A NINA 2,545,373

SELF-BALANCIN PTENTIOMETER CIRCUIT HAVING ILLUMINATED INDICATING DIALFiled May 2. 1945 -3 Sheets-Sheet l 31 @Wil March 13, 1951 2,545,373

A. A. NINA SELF-BALANCING POTENTIOMETER CIRCUIT HAVING ILLUMINATEDINDICATING DIAL Filed May 2, 1945 3 Sheets-Sheet 2 INVENTOR. ANTHONY A.NINA March 13,` 1951 A A NiNA 2,545,375

SELF-BALANCIN PTENTIOMETER CIRCUIT HAVING ILLUMINATED INDICATING DIALman;

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lllllgllllll :ullllllll Illl INVENTOR. ANTHONY A. NINA Patented Mar. 13,1951 A Y Y i??? it.

tential drop across a portion of the potentiometer network at such timesas the network is being recalibrated or standardized.

In the operation of a potentiometer network of the type disclosed above,on the occurrence of a change in temperature of a thermocouple 4, thepotentiometer circuit will be unbalanced to produce a current ow in onedirection or the other through a vibrator which is included along withthe amplifier and designated at 1. The vibrator and amplifier willdetect this unbalance, its direction and amount, and correspondinglyenergize the motor y9 for rotation in the proper direction. The motor ismechanically connected in a mannel` to be described with a contact sothat the latter is shifted along the slidewire I to a position in whichthe potentiometer circuit is again rebalanced and no current flowsthrough the unit 1.

Due to the fact that the strength of the battery 2 gradually diminisheswith use, it becomes necessary to adjust the resistance 3 from time totime in order to maintain the calibrationof the instrument. At suchtimes as the instrument is to be recalibrated or standardized, themovable contact il of switch 9 is shifted to the right to disconnect thethermocouple from the circuit and to insert the standard cell I1 acrossa portion thereof and to simultaneously insert the shunt resistance I5around unit 1. The resistance 3 is then adjusted until the potentialdrop across the slidewire I is brought back to normal. The instrument isthen recalibrated and will continue to function in its normal fashion.

Referring to Figures 1 to 4 inclusive, it will be seen that the variousparts of the potentiometer are placed in a casing I8 that is providedwith a door i9 which is hinged to the front of the casing by means ofhinge pins 20. In the casing there is providedl means to support thebattery 2, the amplifier 1, Yand the standard cell I1, as well asVarious of the resistances. The remaining parts of the mechanismincluding the standardizing rheostat 3 and the switch 9 are mounted onthek door I9. so that these parts may be moved to an accessible positionwhen the door is opened.

`As best seen in Figures 2 and 3 there are provided a plurality of studs2| which extend rearwardly from the door I9 and which have attached tothem a supporting plate 22. Mounted on the supporting plate andprojecting rearwardly therefrom or to the left in Figure 3 is a hollowshaft or bearing 23 which has fastened to its rear end and extendingupwardly therefrom a supporting arm 24. This arm has mounted upon it anannular member 25 made of insulating material around which is wrappedthe slidewire I that takes the form of .a helical coil of lwire which isfastenedto the periphery of the insulating support. It will be seen inFigure 2 that this slide wire extends at an angle to the axis of thesupport 25. The purpose ofthis isv to produce a wiping or slidingengagement with contact 5 as the latter is rotated around the slidewire.This wiping action prevents a groove from being worn in the surface ofthe contact.

The contact 5 is mounted on the outer end of a spring supporting 'arm 26which is attached to and insulated from an arm 21. This latter arm ismounted on a collar 28 which is attached to the rear end of a hollowshaft 29 that is journaled in thebearing 23. Fastened to the front endof shaft 29,is a second collar 3l] that has a driving gear 3| mountedupon it. Gear 3| `meshes with a pinion 32 on the shaft of thepotentiometer 4 motor 8 which is fastened to the rear of supportingplate 22, as best shown in Figures 2 and 3. The collar 30 is provided onits right end with a flange 33 that serves to support an indicatingscale or dial 34. This dial is fastened to the ange by any suitablemeans which are shown herein as being rivets 35. Dial 34 is locatedbehind a window 36 that is formed in the door I9 and cooperates with anindex 31 to indicate the value of the temperature being measured. Theindex 31 is fastened to the front part of a housing 38 which is in turnattached to the plate 22. This housing serves as a reflector for a pairof small light bulbs 39 kwhich may be illuminated so that the scale,which is preferably translucent, may be more easily read. Y

In the normal operation of the potentiometer any unbalance of thepotentiometer circuit which is produced by change in the temperature towhich the thermocouple 4 is subjected, will produce energization ofthemotor 8 in a manner previously described. Rotation of this motor willact through pinion 33 and gear 3| to move contact 5 around the slidewireI to a position at which the potentiometer circuit is again balanced.This same rotation of the contact 5 will cause a movement of dial 34relative to the stationary index 31 so that the value of the temperaturebeing measured may be indicated to an observer in the front of theinstrument.

With instruments of this type it is often desired to control thetemperature which is being measured or to control some other .conditionwhich affects the value of the temperature. This may be accomplishedbythe instrument ofthe present invention by operating a control switchas the contact 5 is moved relative to the slidewire. Ac-

' cordingly, a means is provided in this instrument its lower end. Journaled for rotation in the shaft 42 is a second shaft 45l that has asupporting plate 46 fastened to its rear end. This plate has a forwardlyextending-armg41 that is adapted to bear against the side of arm 43 andsupporting plate 24. There is provided a spring 48 which resilientlyholds the arm 41 against the left side of the support 24 as shown inFigure 4, and there is provided a second spring 49 which holds aprojection on the arm 43 against the arm 41 of plate 46. A switchsupporting bracket 5I is fastened to the rear of plate 46 as is bestshown in Figure 3, and this member supports in it a conventional mercuryswitch 52.

The switch is tilted to be opened and closed by means of a cam 53 thathas a cutout portion or notch 54 which cooperates with theroller 44 tooperate the switch. This cam is mounted on a sleeve 55 that is attachedto the rear end of a shaft 56 which is journaled in the hollow shaft 29.Sleeve v55 has its rightrend formed as the driven member 51 of a conetype clutch and is normally held in engagement with the driving member58 of the clutch that is formed on the left end of collar 28. These twoclutch members are held normally in engagement With each other by meansof a spring 59 that bears with one end against a shoulder formed in theshaft 29 and diuce la counterclockwise `rotation of the indieating ydialyas shown iin Figure 1 or -a clockwise rotation of the cam 53vassh'owninFigo-remi. This rotation of the 'cam will cause the notch 5d to move theroller '44, and the-arm 'carrying this rollen-to the dotted-lineposition shown in Figure 4. Such a Afmovemen't 'would not have anyeiiect on the `position :of the switch since vthe switch s'upo'rt''would remain inthe .position shown `due to the action of Springda.Separation of varm 43 f from arm'd'l will cause flexing fof the spring13S.

If, however,V the 4temperature being measured should drop, cam 53 wouldrotate in a counter1m clockwise direction in Figure "4. During this ro--tationthe notch 54 will pick u'p the'roller '44 and permit it to move ina yclockwise direction rfrom the dotted-line position until the partsreach the positionshown in ful-l lines in the drawing'. Con- K tinuedrotation of cam -53 will move roller "de in a clockwise directionuntil'it reaches the surface of the cam. By this movement the arm@ willtilt the switch supporting member 46 against the action of the springv48 and will `move switch 52 clockwise Aso that the mercury will close4the con"- tacts therein. This-closure may energize suitable relays toproduce the desired 4control action to increase the temperature. Such arelayis shown at R where'it `serves vto operate a switch S qwhich closescircuit lto -a valve V-actuated by `a solenoid SO.

lIn order to have the instrument control the temperature to variousvalues, itis necessary that notch 54 of the cam be moved tokvfariouspositions relati-ve to the position of the contact 5. This may beaccomplished by movingshaft'56` to the left in Figure 3 relative toshaft J29 morder to separate the' clutch members 51 and 58 and the'nrotating the shaft '56. This 'is accomplished by having a frictionmeinberkEZ attached to the front end of ange 6I on'thesh'aft '56.A'co'mple'- mentary-friction member 63 is attached to a shaft 64 whoseother end has mounted upon it a knob 65. The 'shaft 6A is journaled in asuitable be'aring 6B Vthat is fastened in an opening formed in the'dcorI9. Normally the `friction members 62 and"6'3 are held separated amd the'knob is pre vented form rattling by means of a spring 61 that is placedbetween the knob and the vbearing 66. In order to adjustthe'contijolpoint of the instrument, the knob 65 is moved to the left in Figure 3until the yfriction membersA 62v and "63 engage. lurthe'r movement willovercome the force of 'the spring 59 and separate the clutch memberssothat the `cam maybe rotated 'rela tive to the contact. In order that thecontrol point of the jinstrumentmay Vbe seen and maybe accurately set,there is provided a pointer s'ftnat soirs-ets will 10e-operated. s

i n win yte seen from Fig met 'the` landieatin'gdrei hat-uisperature'fis lindioated'as'being fat"6-.3 and this is i als'ofth'econtrol -point since that fthe `.poi-nt'on sc'aief'lfl lto whichthepointerisadiustd. Suppos'e.fhoweve1f,a 'furnace' under cohtrolis-just be: ing 1 started up. In this v"condition 5the Izero -r'narkon'the scale 'H would'be under :pointer 3ilfand unless some Vother meansthan the 'pointer y 6B wereiprdvidedfitwoufld impossibleto-teli wherethe controlapoiiit of:the'instruinentwasset. Since, however,thelpointer- 'is\d'ispl-ace"d '180` from pointer T68 Land the/*scale tl2is displaced'1180o `from the scale it, an `lobserver' will be Vable to1Asee the control point 'of the'instrument no matter what the positionof the dial; since;- lif the temperature vindicated lbyscale il is zero,the small fend of pointer 159 will be visible through opening `*36 -aswill the :portion `of scale ft2 `with which -co operates. l. Y i l Thereis falso provided' -on the front of the instrument a knob 'i3 by meansofwhichthe stand: ardizing rheostat f3 andswitch) may be adjusted and aknob -14 whichfoper-ates -afswitch that can turn onor -oii the -entireystem. There is also provided -afsuitableknob i5, which maycontainalock, byLmeans ofwhich door i9 may beopened or closed. N i

In Figure 5 -thereisshown-another embodiment of -the invention. In thisembodiment the case i8 also has'supportedY-in it theamplifier unit asweil asy the two batteries. lThe door I9 in this embodiment is fastenedto vthe lcase by suitable screws, asfshown in the ydrawing; rather thanbe'- ing hinged theretofas Ywas Ythe door in-'the :previously describedembodiment. The mechanism is, hcweveryattached to the inside of the'door in a manner sirnilar'to Athat 'previously described. In thisVerribo'd-iment :there are provided `studs li which project rearwardlyfrom the door varidv to which is yattached Va supporting .plate 11. Thisplate `has fastened in lit -a rearwardly extending bearing 18 formedwith 'a 'ange 19 to which is attached *by tany' suitable-means yaninsulating disc y8i The 'siidewi're l is 'wrappedla'roundthis disc. f Y

The arm`21 upon which iide'wire 'contact 5 is'ndtisfa-stedto a tubularshaft 83. This shaft extends through the bearing 18 and projects fromthe front portion thereof where it has mounted on it a collar 84.Rotation is imparted toshaft 83 and the slidewire contact by a drivegear 85 which is attached to collar 84. Gear 85 is in mesh with thepinion 32 on the shaft of motor 8. The collar 84 also has on it a flange.8B to which is attached a suitable indicating dial 81 that in this caseis dished as shown in the drawing and for a purpose which will bedescribed below. It is noted that this dial will have only one scale onit.

In this embodiment the control switch 52 and its support are mounted ona yoke 88 that is pivotally mounted upon a sleeve 90 which is fastenedin the supporting plate 11. The yoke has formed as arportion thereof anarm 89 which engages one end of a lever 92 that is mounted upon shaft 9|which is journaled in the sleeve 90. The lower end of arm 92 has a pinprojecting from it and rotatably mounted on the pin-is a roller 93 whichengages the switch actuating cam. There is provided a spring 94 whichnormally biases the switch supporting yoke 88 to a xed position againsta portion of the plate 11 whereby the switch will be held in ahorizontal position similar to the position in which it was held in theembodiment of Figure 1. There is also provided a spring 95 which servesto hold the upper end of the lever 92 against the portion 89 of yoke 88.

Arm 92 is moved to throw the switch by means of a cam 96 that is mountedonV a second collar 91 which is journaled on the collar 34. This collar91 also carries a gear 98 by means of which the cam may be rotatedrelative to the shaft 83 carrying the slidewire contact, in order toadjust the control point of the instrument. Normally, however, thecollars 91 and 84 are held in a xed position relative to each other bymeans of a. friction spring 99 which extends between the cam 96 and thegear 85. Gear 98 is rotated to adjust the control point of theinstrument by a pinion IOI which is formed with a sleeve |02 andwhich isjournaled for rotation on a shaft |03 that is in turn rotatable inopenings formed in door I9 and supporting plate 11. The shaft |03 hasmounted on it adisc |04 to the right side of which is attached a washer|05 of friction material. Also on shaft |03 is a knob |08 by which thisshaft may be moved axially and rotated. Normally the shaft is held inthe axial position' shown with washer |05 separated from pinion IGI by aspring |01 that is fastened to the rear face'of the supporting plate 11.

In order to adjust the control point in this embodiment of theinstrument, the knob |06 is moved to the left in Figure 5 until thefriction washer |05 bears against the face of pinion IOI. Thereafterknob |06 is rotated to rotate this pinion and the gear 98 in meshtherewith. Such rotative movement produces relative rotation between thesleeves 91 and 84 so that the cam 96 may be rotated relative to thecontact 5 and thereby adjust the control point of the instrument.Inorder to prevent rotation of the gear 85 and driving pinion 32 whenthe control point of the instrument is being adjusted, there is provideda brake member I 08 that is mounted on a stud |09 fastened to the lowerportion of the plate 11.V This brake member is held normally in theposition shown by a spring I I I but may be moved to the left intoengagement with the pinion by a disc I I2 which is attached to thepinion IIJ I In this embodiment of the invention the door I9 is providedwith-a circular-opening in which is .c 8 inserted a bezel I I3 that hasa window I I4 mounted in it. The window is of such a size that theentire disc 81 is visible. There is-provided an index member I I5 whichis attached to the door I 0 that cooperates with the disc 81 in order toindicate the Value of the temperature being measured. In order toindicate the control point for which the instrument has been adjusted,there isprovided a pointer IIB which is attached to the gear 98 andwhich extends forwardly and upwardly so that the pointer lies in frontof the edge of the disc 81. Normally, ofcourse, gear 98 rotates with thedisc, so that those parts retain their adjusted position relative toeach other, and since the window II4 is circular, the pointer II6 may beseen at all positions of the disc 81;

In this embodiment of the invention illumination for the disc 81 isprovided by means of a bulb III. This bulb is'mounted in a socket II8that is fastened to the interior ofthe shaft 83. Since the disc 81 isdished, the entire surface of this disc will be illuminated and may,therefore, more readily be seen. To prevent glare in the eyes of anobserver, there is provided a coating II9 of some suitablev material onthe back of the window IIII. This material preferably will be such thatit can reflect light from the bulb back to the disc. Since socket I I8is attached to shaft 83, the cable I ZI carrying current to the bulbwill be twisted slightly as the disc is rotated. This twisting, however,will not be objectionable since the disc 81 is only being rotatedapproximately 320 through its full range of movement.

From the above description, it will be seen that I have provided acompact, self-balancing potentiometerwhich has a simple and accuratecontrol mechanism attached to it. The means illustrated herein foradjusting the control point of the condition and for indicating thevalue'o'f the condition, as well as the value of the control point, isboth simple and eiective.

While in accordanceV with the provisions of the statutes, I haveillustrated and described the best forms of the invention now known tome, it will be apparent to those skilled in the art that changes maybemade in the form of the apparatus disclosed without departing from thespirit of the invention as set forth in the appended claims, and that insome cases certain features of the invention may sometimes be used toadvantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent is:

-1. In a measuring and control instrument, a support having a bearingtherein, a slidewire mounted on said support, control means mounted onsaid support, a hollow shaft journaled in said bearing and extendingbeyond both ends of the same, a contact engaging said slidewire carriedby one end of said hollow shaft, drive means carried by the opposite endof said hollow shaft whereby said hollow shaft may be rotated Vto movesaid contact along said slidewire, a second shaft journaled for rotationin said hollow shaft, means to operate said control means mounted onsaid second shaft, mechanism operative to keep normally said shafts fromrotating relative to each other, and meansto relatively rotate'saidsecond shaft and said hollow shaft whereby said operating meansV may beadjusted relative to said contact. Y

2. In a measuring and control instrument, a support having a bearingtherein, a circular slidetationgin saidtbearing meansftoamountsaldi-con.-

tact, on ,said hollow shaft-.sof that as.: said. shaft istl rotated..`said: contachwillibe moved, along), said slidewire;l means;V to` lrotate.-.said.,hollew shaft.v1 to positions-V de-pendentauponf-the valuaof amaniable conditiorh. a second. shaft: v;ournal.edfor rotation insaidfhollow shaft, meansgto operata said conf trol meanscarriedtbysaid.- second,l shaftiiawclutch comprising. a part on.-eaehrofsaidshafts; resilient means-operativeftoa-maintain normally saidclutchpantsiin engagementwth each-.othenfandfmeans toAseparatefsaid,clutchfparts:andmotateisaidfsecf ond^ shaft'relativefto.said; hol1ow-.'shaftwhereby said: means'to oper-atefsaid,control-meansimait be adjusted relative tosaid-contact.

3.-. In a measuringv and, control. instrument.. a support .havinga;hearingthereim,acircularfslide wireriixedffrelative toe-saidupport.,control means fixed.- relative lto-saidt supporte` a..contact: engagingsaid slidewre; a'..hollowtshaft-zrotatably mounted in.` saidLbearingnmeansi tmount-fsaidcontarct on said; hol1ow.: shaft.tor-be.rotatmitherewithg; means toirotate saidghollowfzshaft'zto;positions, depend;- p

ing; uponf theavalue fon azevariablefconditiom,anfindicatingc dial;carried byfsaidfisliaiintof` indicatefby its position. the.value2ofitheconditiona asecond shafii mounted;V coaxiallyoffs.said;hollow:y shaft,

means.. to operatav saidicontrol".E means vcarriedi byv said secondi'.sham-.zV clutcht means -z having3W ai: part ony each l offsaith-shafts;Y` meanszt'o.y keepfnormally saidrpar-ts in`eng-agementwhereby said shafts will rotate togethers;means-fftotseparata tha parts ofsaid" clutchtandrotatevsaidi secondshaft':.rre1a; tive'to -said" hollow f shaft; and means =carried=by saidsecondshaftff andl cooperatingawith: saidr indicating dialatoentri-bitthe relation ofsaidf'means to\operate said controlmeanseandtsaid'l Contact;

4:' In" a measuringI andi controi-" instrumentgf a casing; a doorforsaid"casing; aecircular-fsiidewire mountedin lfiXed@relationttosaiddon'adirst shaft journalediforrotation reiative to said door),aicontactrcarriedrby-said ifsifshafiand engaging said; slidewire` tobermoveditherealong; control meansv fixed relativeto Asaid door; asecondshaft coaxialzwithisaid rstshaft? means to actuate saidcontrol"m'eanscarried bysaid^1secondfshaft, aV clutchV havinga partthereof on--each'hv shaft', means to keepnormally'saidclutchrpartsin^enf vgagernentwiti'iA eachf other;-'a-"thirdf shaft slidably" androtatabiyrmountedeirr-saidf' door coaxial with said" rstftwo shafts;andi-*means to' move said thirdshaft' 'intoengagementewitlr oneeofsaidfirst" two shafts to" separate` said'z clutch? partsand rotate onefof`saidlfirst ltwo`shafts'"rel'ativeto the y other.

tate' s: iidv hollow.. shaft to. a @position corresponda ing to. .the`value. .of a .variabld condition, `control means mountedlon said;`dor,.a.secondf'shaft con-- centric; with sadjhollowY shaft;- ..mea.ns...to`-operate saidontrol.meansarriedbit saidsecondhaft, clutch means,having;.aanar.tgthereofion.. each., of

saidfshaf-tsfmeansto. hold normallythe; parts of t said clutchineansinengagement. with. eachl other, means.A mountedzlin said:V door coaxialwith said Vshalt-ts tof-separate. said.- clutch'. par-ts and rotateone-of said-shaftsrelative ltothe other; and means tofindicatethefrelative position osaid=shaf-ts-.r

^ 6. In. a: measuring. and.' controlz instrument a support,..a circularslidewire mounted. on. said support;Y acontact to engage saidslidewirei;a hol-low shaft journaled-` in saidsupport;` means to mount. said-Acontact on said shaft-fon rotation therewith; control means: mounted:onfsaid'I suppor-tg` a: second* shaft journaledin said hollow shatt'"means to operate said-control means carrriedz-by said secondshaftavzclutch having a part thereofronzveaclr, of'. saidishaftsg; saidclutch` being engaged on disengagedrby axial movement ofV said secondyshaftrmeans to keep' normallyfsaid clutch engaged.; ciilt'ch operating".means mounted `co axial. 'withf" said lshafta and means 'byl winch'.said clutciiioperatingrrreans may be operated".Y to :shift said secondshaft axiallyandto'rotate'thesaine.

'7.1 Ina-measuring. instrument', afcasing; ai window in'fsaid casing:and`l heingf generally 'semi-'cincularzf inf` shape',V an indicatingiYdial? backi of said window; said'dial.beingcirculan meanstoirotate said"dial" to positions; proportionalA toy the valueof'aiconditionlbeingmeasured; a pair of concentric' circular@ scales'oni saidf'diafl said" scales beingdisplaced ifi'omi'eachother; a memberat'- tached tof said casingf and'icooperatingfwith the outerfofV said'scalesetoindicatethe value' of 'a condition; af pointer'concentricwithLsaidf dial and movable-therewith, said pointer-*having a-*port'ioncooperating-'withfsaidffouterscale tov indicateY the desiredfvalue ofthe'nondition, and another portion cooperating with thecorrespondingportion of 'thevlinner of said*concentricv scales whereby the desiredValue of -the condition" maybe indi; catedthroughsaid' window to anobserver' no linatter what tlief valuerof th'efcon'dition'maybe;

8f InA ermeasuring' and' control instrument', a casingf'having 'anropenfront', a doorto" close the openefitontf ofsaid'casing', asupport onsaididoor, a'bearing projecting from' said" support', Ya circularslidwire'mounted' on' said bearing, a Contact toengage'saidi'slidewire;a shaft "journaled in' said bearing; means.` to attach. said contacttofsaid shaft"fonrotationtherewith; motor means'to ro# tate said'shaftandthereby movei saidcontact along said slidewire to apositionlproportional to the'value ofa. conditiomzcontrol (means mounted onsaidlsupp'ort, a cam to operate said control means,. means to mount'saidicam on saidlshaft for 'rotation'.relative thereto, means to.keepnorr'nalli7 said cam from'. rotating relative. to said shaft, ,meansto'rotate saidicamon'said'shaft to change its position relative'tsaidlcontact and thereby 'adjust the. control. point ofjsaid"instrument;v and"' brake' meansV operated by, said lastmentioned'imeans` to preventsaid 'shaft .from .rotatingas said'cam isbeingadjusted.

i 9'.`` I'ni a. compact,` self -b'alan'cing potentiometer tlypecont'rolliinstrument,L including: acasing having a movable cover.;apotentiometer. network including...as1idewire ,mounted.on..said cover,.a

contact mounted. on said cover. andA engaging said. .s1dewire,v. and; a.plurality of. resistances mountedlon .said cover.; .amotor mountedonsaid cover. and i energized. for. rotation. in --one direction.v 01.`an. opposite.. direction, towards the posi?Y tion inwhich.saidcontactbalances said potenf tometer.network,.saidmovement.depending upon yunbalanxe oilsaid..potentiometennetworle a-shaftrotated by said motor to move said contact along said slidewire; an armbetween said shaft and said contact; a condition-responsive elementlocated outside of said casing and connected to saidy potentiometernetwork; an electric switch for connecting a condition-adjustingmechanism to a source of electric power for operation and fordisconnecting said mechanism from said source of power; the combinationincluding: a scale having a plurality of markings on it and driven` bysaid shaft so as to be moved as said shaft rotates; a stationary indexcooperating with the markings on said scale to indicate that value ofthe condition to which said conditionresponsive element is responding; acam for actuating said electricY switch to open or to closed position; anormally engaged clutch forming part of the driving connection betweensaid shaft and said cam; a pointer movable relative to said scale toindicate the value of the condition at which said cam is set to actuatesaid electric switch and movable by said shaft when said shaft movessaid scale so that said pointer retains the positionrelative to saidscale to which it has been set; a normally disengaged clutch for movingsaid pointer and said cam while said scale remains stationary to adjustthe position at which the cam is set to actuate said electric switch andto adjust the indication of theV set point given by said pointerrelative to said scale; and a manually operable handle extending outsideof saidcasingand -operable to disengage said normally engaged clutch topermit said contact and said scale to remain stationary andsimultaneously to engage said normally disengaged clutch to adjust saidpointer to indicate the value of the condition at which value said camis set t actuate said switch and to adjust said cam relative tosaidswitch.

10. In a potentiometer type control instrument, including, a casingincluding a cover for said instrument, a balanceable potentiometernetwork including, a slide wire, a contact movable over said slide wire,a cell to impress a potential on said slide wire, said parts beingenclosed in said casing; a condition-responsive means connected to saidnetwork and located outside of said casing; a shaft connected torelatively move said slide wire and contact; motor means operating uponunbalance oi' said network to rotate Said shaft to relatively move saidslide wire and Contact to rebalance said network; control means for thecondition to Vwhich said condition-responsive means is responsive; thecombination including: a scale mounted on said shaft so as to be driventhereby, a stationary index cooperating with saidscale to indicate thepresent value of said condition, an actuator for driving said` controlmeans from one operative position to another, a set point indicatorconnected to said actuator for indicating the value of the condition atwhich said actuator drives said control means, a normally engaged clutchforming part of the driving connection between said shaft and saidactuator, a handle rotatably andslidably mounted in said cover andextending outside of said cover and operable to disengage said clutchand toengage said actuator and said set point indicating means whilesaid scale remains at rest, anda brake member movable by said handle tohold said contact and said scale stationaryduring the movement of saidhandle to adjust said indicator and said actuator.

11. In a measuring instrument having a plurality of component partsincluding, a control element for controlling the magnitude of a conLdition, a slide wire, a contact moving in engagementv withysaid slidewire, a cell to impress a potential upon said slide wire, a casingincluding a cover Aenclosing the various component parts, a motor meansalso in said casing and operable in response to network unbalance tomove said contact relative to said slide wire to a position in whichvsaid network in rebalanced: the combination including, a shaft drivenlby said motor, a scale driven by said shaft, a stationary indexVcooperating with said scale to indicate the value of the condition atwhich said network is balanced, normally engaged disengagable drivingmeans driven by said shaft, an actuator for moving said control elementfrom one position to another, an indicator connected to said actuatorand cooperating with said scale to indicate the value of the conditionto which said actuator drives said control element, a handle located insaid cover and operable from the exterior thereof to disengage saiddriving means, whereby said actuator and said indicator may be adjustedwithout disturbing movement of said scale, and a normally engagedslipping journal, said actuator and said indicator having said slippingjournal'in the connection between them and vsaid contactand'said scale,whereby said handle can move said indicator and saidactuator while saidcontact and said scale remain stationary.

l2. In a measuring instrument, a support, `a shaft rotatably mounted onsaid support, a motor operating said shaft in response to a variablewhich is to be measured, a scale on said shaft, a stationary indexcooperating with said scale to indicate the instantaneous value of avariable, an electric switch for connecting a'variable-adjustingmechanism to a source of electric power for operation and fordisconnecting said mechanismfrom said source of power, a cam foractuating said electric switch to open or closed "position, a pointerconnected to said cam to indicate the value of the variable at whichsaid cam is set to actuate said electric switch and movable by saidshaft when said shaft moves said scale so that said pointer retains theposition relative to said scale to which it has been set, and a manuallyoperable handle extending through said support and operable to adjustsaid Y pointer relative to said scale and to adjust said cam relative tosaid switch. l

i 13. In a self-balancing measuring instrument having acondition-responsive clement: a casing having a movable cover; apotentiometer network including, a slide wire, a contact engaging saidslide wire, and an electrolytic cell supplying a potential to said slidewire, a plurality of resistances, and a motor responsiver to unbalancein said network and movable to move said contact relative to said slidewire to a position in which said network is rebalanced; saidcondition-responsive element being located outside of said casing andconnected to said potentiometer network; ,an electric switch forconnectinga condition-adjusting mechanism to a source of electric powerforv operation and for disconnecting said mechanism from said source ofpower, a scale having a plurality of markings on it and driven by saidmotor, a stationary index designating that marking on said scale whichindicates the value of the condition to which said condition-responsiveelement is responding; a cam ior actuating said electric switch to openor closed position; a pointer connected to said cam and movable relativeto said scale to indicate the value of the said open side, a portion ofsaid door being transparent, a scale mounted on said door and driven bythe movements of said element past said transparent portion, an indexmounted adjacent said scale so as to cooperate with said scale so as toindicate the present value of the variable as measured by said element,an indicator mounted on said door and movable by said Vmeasuring elementin conjunction with said scale and having a portion cooperating withsaid scale so that the reading of said indicator against said scale doesnot vary during the joint movement of said scale and said indicator, anormally engaged clutch mounted on said door and forming part of thedriving connection between said element and said device, and a hand knobmounted for engagement with said clutch to disenage said clutch and toturn said indicator relative to said scale and to vary the value of thevariable at which said element operates said device while said scale andsaid element remain stationary.

20. A control instrument for automatically effecting a control action ona variable and for indicating the present value of said variable and thevalue of said variable at which said control action is taken and havinga measuring element responsive to said variable and having a iinalcontrol device for controlling said variable and operable by saidmeasuring element at a selected value of said variable, the combinationincluding: a casing having a flat wall and sides projecting from saidflat wall and encircling a front opening, a door mounted on said casingfor relative movement therebetween and normally closing said frontopening, a transparent window vforming a portion of said door, a scalemounted on said door and movable past said window under the drive ofsaid measuring element, a stationary index visible adjacent said windowand cooperating with said scale to indicate on said scale the value ofthe variable measured at that moment, normally engaged relativelymovable driving and driven elements forming part of the drivingconnection between said measuring element and said `final controldevice, an indicator connected to said drivenrelement and having aportion cooperating with said scale and visible through said window toindicate by reference to said scale the value of the variable at whichsaid measuring element operates said control device, and a manuallyoperable handle mounted on and projecting through said door andconvenient to the hand of an operator looking through said window, saidhandle being operable to disengage said means and to turn said indicatorWhile said measuring element and said scale remain stationary.

21. In a measuring andcontrol instrument, a casing-having a at wall andsides projecting from said iiat wall vand encircling a front opensaidfront opening, a transparent window forming a portion of said door, asupport mounted on the inner side of said door, potentiometer mechanismincluding a slide wire, a contact, a driving motor, and a scale platemounted on said support, said scale plate being movable past said windowunder the drive of said potentiometer mechanism, a stationary indexvisible adjacent said window and cooperating with said scale to indicatethe value or" the variable measured at the moment, control mechanismmounted on said support and operated by said potentiometer mechanism,control point adjusting means for said control mechanism, and a manuallyoperable handle attached to and extending through said door tb adjustthe control point of said mechanism from the outside of said door.

22. In an instrument as defined in claim 21, the combination whereinsaid control mechanism includes a bearing projecting from said support,a hollow shaft journalled in said bearing, illuminating means for saidscale plate carried in the bore of said hollow shaft, and an opaquereflector mounted on said window and located opopsite said illuminatingmeans so as to shield it from the direct view of an observer.

ANTHONY A. NINA.

\ REFERENCES CITED The following references are of recordin the file ofthis patent:

UNITED STATES PATENTS Number Name f Date 1,907,093 Shivers May 2, 19331,931,223 Harrison Oct. 17, 1933 1,942,343 Melik-Minassiantz Jan. 2,1934 2,096,064 Ross et al. Oct. 19, 1937 2,112,704 Mackay Mar. 29, 19382,152,635 Crane et al Apr. 4, 1939 2,158,468 McCleary May 16, 19392,277,365 Michael Mar. 24, 1942 2,288,679 v Caldwell July 7, 19422,368,912 Barnes Feb. 6, 1945 2,406,341 Beach et al Aug. 27, 1946FOREIGN PATENTS Number Country Date 12,416 Great Britain Sept. 20, 1906569,873 Germany Feb. 9, 1933 OTHER REFERENCES Handbook of IndustrialTemperature and Humidity Measurement and Control, Behar, 1st ed.,`Instruments Publishing Company, Pittsburgh, 1932, pp. 231, 232, and372.

